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Rose diagram

Can someone comment on technical explanation of the wind rose attached?

I can understand the wind is blowing between WNW & SSW with speed of 7-11 km/h. For frequency of 11-16 km/h its blowing from SW & SSW. For frequency of 4-7 km/h its blowing between WNW & ESE?

Is this all or some info I am missing? What do the spikes mean?

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  • $\begingroup$ This wind rose tells me to build the primary runway 07/25 and a secondary 18/36, but that's just the pilot in me talking. $\endgroup$ – casey Jan 30 '16 at 2:47
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The wind rose shows quite a few things. The goal of a wind rose is to help you understand the frequency, strength, and direction the wind comes from.

Why the direction the wind is from, and not to? Well, they are often used to visualize data for building design, and there we care about resisting loads, so we use the direction the wind comes from. They are also used in meteorology: different winds bring different weather (north winds are cold in the Northern hemisphere), and so it makes sense to use from there as well. Aviators care about the winds they will encounter taking off or landing, and so they want to know what they have to resist. There are many more reasons, some of which are discussed at https://en.wikipedia.org/wiki/Wind_rose.

Some other things to know as you look at the chart:

  • This chart is based on a time series of winds at the location.
  • The data have been placed ('binned') into wind speed ranges, and direction ranges. For example, a recorded wind speed and direction of 12.6 km/hr from 92° will be placed into the 11-16 km/hr wind speed range, and W direction range. This makes it much easier to take in the results.
  • The different coloured lines are for the different wind speed ranges, measured in kilometers per hour.
  • Winds are shown in small sectors of wind direction. In this plot the bins are 22.5°, which corresponds to 16 subdivisions of the compass rose.
  • The distance from the center of the rose gives the frequency of winds in each wind direction sector; this is why the north axis has a number on it that increases from 0 to 4000; this is the number of records.

To use the wind rose, you can start by looking at winds of a certain speed range, for example the pale green series. This is winds in the range 7-11 km/hr. Now, follow it clockwise around the plot. You see that there is a peak in winds with a speed of 7-11 km/hr to the north, another to the E, and also a lot of 7-11 km/hr winds between WNW and SSE.

You could also look at a particular wind direction, for example for winds from the west. Maybe your building has a very exposed west wall? Anyway, you would see then that the most common winds are in the range 7-11 km/hr (green line), followed by 11-16 km/hr (purple), then 4-7 km/hr (red), then 0-4 km/hr (blue), and so-on.

If we wanted to, we could get the relative frequency of winds in this sector by looking at the distance from the center of the plot for each line and dividing the distance for one line by the sum of all lines in that direction sector.

We can also see some information about the maximum wind speed. For example, there are no winds over 22 km/hr at this location, because there is no orange line. But, there is a light blue line, which shows winds from 16-22 km/hr, so we can say that the maximum wind speed that's been see at this location is less than 22 km/hr, but more than 16 km/hr.

This wind rose is quite hard to use. Often we would plot the wind speeds as stacked bars so that you can see what is the direction from which winds come most often. This is used in wind energy, for example. See https://stackoverflow.com/questions/17266780/wind-rose-with-ggplot-r for an example of a different way to show this data.

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No, you've misunderstood it. There's lots of information you're missing. Every data point is information, and you've listed a tiny proportion of them.

Furthermore, 4-7 km/h and 11-16 km/h aren't frequencies at all, they're wind speeds. The distance from the centre gives you the frequency.

So the spike towards N means that North winds are much much more frequent than the NNW and NNE winds. There may be some protection in those directions such that the winds that would come from there, are actually getting channelled to come from the North instead. Or there's a particular time-of-day effect, or a recording artifact, or one of a dozen other explanations that only someone with more information about the site and the data collection could assess.

However, the fastest winds don't blow from that direction at all: they're all coming from the quadrant between S and W.

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  • $\begingroup$ Thanks alot for correction. What about 4-7 km/h wind speeds. Are they uniformly distributed from W to E? Can you suggest some good source for learning wind roses? $\endgroup$ – Jahangir Jan 29 '16 at 15:39
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    $\begingroup$ You can answer your own question re 4-7 km/h, which is the darker red line: is it as far from the centre in the Westerly direction as the Easterly? Use the concentric rings to judge. The best way to learn them is to collect your own data and then make your own wind rose. The second best way is to use someone else's data and then make your own wind rose. $\endgroup$ – EnergyNumbers Jan 29 '16 at 17:20

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